[Epithelial-mesenchymal transition of prostate cancer: cancer stem cells or bulk cancer cells].

Objective: To test the hypothesis that epithelial-mesenchymal transition (EMT) of prostate cancer is most likely to occur in cancer stem cells (CSC).

Methods: The isolation of CSC from LNCaP cell line was performed by flow cytometry based on side-population (SP) phenotype. After SP sorting, LNCaP/SP and LNCaP/NSP were used for further transfection of hypoxia-inducible factor-1α (HIF-1α). Subsequently, EMT-associated proteins were detected by Western blotting. And the assays of Transwell and methyl thiazolyl tetrazolium (MTT) were used to compare invasive and proliferative potency between LNCaP/SP and LNCaP/NSP after HIF-1α induction. Eventually, xenograft experiments were performed with LNCaP/HIF-1α/SP and LNCaP/HIF-1α/NSP cells for further analysis of in vivo tumorigenesis and distant metastasis.

Results: Through HIF-1α-induced EMT, LNCaP/HIF-1α/SP exhibited such remarkable EMT characteristics as a positive expression of epithelial markers (E-cadherin and CK18) and a negative expression of mesenchymal markers (vimentin, N-cadherin, fibronectin, cathepsin D, MMP-2 and uPAR). And LNCaP/HIF-1α/NSP underwent partial EMT with an abnormal expression of some mesenchymal proteins (vimentin and cathepsin D) and loss of epithelial protein (CK18) despite reservation of another important epithelial marker (E-cadherin). Further Transwell and MTT assays indicated that LNCaP/HIF-1α/SP exhibited stronger in vitro invasive and proliferative potency than LNCaP/HIF-1α/NSP cells. In animal models, the volume of subcutaneous tumor by LNCaP/HIF-1α/SP cells was much greater than that by LNCaP/HIF-1α/NSP counterparts ((1008 ± 230) vs (288 ± 145) mm(3), P < 0.01). Moreover, LNCaP/HIF-1α/SP cells also had a significantly higher rate of subcutaneous tumor incidence (80% vs 53%, P < 0.05) and bone metastasis (40% vs 0, P < 0.01) as compared with LNCaP/HIF-1α/NSP counterparts.

Conclusion: As the main target cells of prostatic EMT, CSCs may develop a more malignant phenotype after EMT.